Ford: overheating, clutch fan, target practice

Question
I got one for you. I have a 1990 Mustang 5.0 GT. When I bought it,it was overheating,so this is what I have done. New radiator,new water pump ( flushed the block with air pressure and water & flushed out the heater core ) with the cap off it flows good in the radiator, three different new thermostats one 180* & two 195's , all new hoses, new drive belt & made sure it was on right, I even put on a new clutch fan. Now here is the kicker, if you leave the thermostat in it,it overheats everytime, but if you take the thermostat out it runs fine. Have done all the vaper locking tricks that I no of, dont seem to be the problem. But living in NY, I need heat. The car runs strong, dont miss or smoke white smoke, have checked all spark plugs for moisture, none, so I dont think that it has a blowed head gasket. Checked the back of the intake, no leaking that I can see.It's not leaking anti-freeze anywhere, although I do get that sweet hot smell sometimes. I did the old trick of taking the guts out of the thermostat to slow it down some, and now it gets to 130 degrees and stay there. I have played with Mustangs for years, in fact I own a 1965 coupe also,with a 289, but this one has me to the point of using the car for target practice. What am I missing? Can you save the car from 9mm holes?  Jim  

Answer
Jim ran into this problem  2x's  ready for this it was the F*%#$@ing rad. cap.  Cust. did every thing you did but never replace the cap . what i want you to do is when it is running see if the lower or upper hose collapse  also pressure test the cap.feel the hoses and see if they are both the same temp.let me know.